Vehicle designers strive to power vehicles with highly fuel efficient engines or other power sources. Multiple linkage systems connecting a crankshaft, an eccentric shaft and a piston are configured to move the piston within a cylinder according to a selected four-stroke working cycle, such as an Atkinson cycle. While suitable for their intended purposes, these multiple linkage systems constrain movement of the piston to only one four-stroke working cycle.
As used herein, an Atkinson cycle is a four-stroke cycle with an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke, with the expansion stroke longer than the compression stroke (i.e., an expansion volume greater than a compression volume). The expansion ratio of a four-stroke working cycle is the ratio of the volume of the expansion stroke to the volume of the compression stroke. For cylindrical working chambers, this is the same as the ratio of the length of the expansion stroke to the length of the compression stroke. An Atkinson cycle has an expansion ratio greater than 1.
A true Atkinson cycle engine reduces pumping compared to a “pseudo Atkinson cycle” engine, which is a conventional Otto cycle engine with an expansion ratio of one and late intake valve closing. A true Atkinson cycle reduces the pumping losses associated with pulling air/fuel mixture into the cylinder and then pumping it back out during the compression stroke, which is inherent in a pseudo Atkinson cycle engine with late intake valve closing. References herein to an Atkinson cycle engine means a true Atkinson cycle, not a pseudo-Atkinson cycle engine. Atkinson cycle engines typically have lower power than Otto cycle engines, so a larger displacement engine is required to provide the same level of power for wide open throttle performance.